1. { INTRODUCTION APPROACH
PEO-Based Hybrid Hydrogels with Hairy Nanoparticles as Polyfunctional Crosslinker
Jessica A. Ellett, Roger A. E. Wright, and Bin Zhao
Department of Chemistry, University of Tennessee, Knoxville, TN 37996
INTRODUCTION
II. Synthesis of Free Chain Transfer Agent
Hydrogels, consisting of a crosslinked 3-dimensional (3D) polymeric network swollen with water, are used in multiple applications such as drug delivery, chemical sensing, and tissue engineering. Synthetic hydrogels, however, tend to be brittle and lack toughness. It has been shown that both high network uniformity and the incorporation of nanoparticles can enhance the mechanical properties of hydrogels.1,2 This work is aimed at fabricating hybrid hydrogels with advanced mechanical properties using thiol-terminated polymer brush-grafted silica nanoparticles (hairy nanoparticles) as polyfunctional crosslinker to react with allyl end-functionalized poly(ethylene oxide) (PEO) via “thiol-ene” click chemistry. By synthesizing these mechanically advanced hydrogels, new research, and thus technology, can begin to develop in many fields. b d c a c c c d c a b
Figure 3. 1H NMR spectrum of chain transfer agent benzyl dithiobenzoate (BDB).
APPROACH
Step 1: End Functionalization of Poly(ethylene oxide)
III. RAFT Polymerization of DEGEA with AIBN and BDB.
DEGEA
Step 2: Synthesis of Hairy Nanoparticles
PDEGEA
aminolysis
hydrazine
RAFT
- SH
Step 3: Synthesis of Hydrogels by ‘Thiol-Ene’ Click Chemistry
Figure 4. 1H NMR spectrum of the RAFT polymerization mixture at a monomer conversion of 39.3%.
Figure 5. GPC of PDEGEA after 2.5 h.
AIBN
IV. Immobilization – CTA and Thiol Silanes +
Immobilization of the chain transfer agent onto 15 nm silica nanoparticles.
Immobilization of (3-mercaptopropyl) triethoxysilane onto 15 nm silica nanoparticles
Step 1: End Functionalization of PEO
- SH a e b b { c c e a
Step 3: Test Synthesis of Hydrogels – Photoinitiated v. Thermoinitiated d d
Thermo-initiated cross-linking of allyl end-functionalized PEO with thiol-immobilized nanoparticles
Photoinitated cross-linking of allyl end-functionalized PEO with thiol-immobilized nanoparticles
Free standing gel
Blue lines are PEO chains
AIBN h a c b e
No free standing gel
75° C
Figure 1. 1H NMR of allyl end-functionalized PEO with a molecular weight of 10,000 g/mol.
SUMMARY
Step 2: Synthesis of Hairy Nanoparticles
I: Synthesis of Benzyl Dithiobenzoate-Terminated Silane
Allyl end-functionalized PEOs have been successfully synthesized.
All components necessary for surface-initiated RAFT polymerization, including
the benzyl dithiobenzoate-terminated triethoxysilane and free CTA, have been
prepared.
Benzyl dithiobenzoate-terminated triethoxysilane and (3-mercaptopropyl)
triethoxysilane have been immobilized onto the surface of two different sets of
silica nanoparticles, which are 15 nm in diameter.
The hydrogel synthesis has been successfully tested with thiol-functionalized
silica nanoparticles using thermal initiation. More work will be accomplished to
optimize the conditions for gel synthesis.
The final product benzyl dithiobenzoate-terminated triethoxysilane is a light red liquid. i f e a b h c
References:
Cui, J.; Lackey, M. A.; Madkour, A. E.; Saffer, E. M.; Griffin, D. M.; Bhatia, S. R.; Crosby, A. J.; Tew, G. N. Biomacromolecules 2012, 13 (3),
2. Haraguchi, K. and Takahisa, T. Adv. Mater. 2002, 14 (6), c j g d c i f d
ACKNOWLEDGEMENTS e c g j
National Science Foundation
University of Tennessee
University of North Georgia h b a .
Figure 2. 1H NMR spectrum of benzyl dithiobenzoate-terminated triethoxysilane.